767  
FXUS02 KWBC 071725  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1224 PM EST WED MAR 07 2018  
 
VALID 12Z SAT MAR 10 2018 - 12Z WED MAR 14 2018  
 
...MODEL GUIDANCE CONTINUES TO OFFER A WIDE RANGE OF SOLUTIONS  
WITH ANOTHER STORM DEEPENING OFF THE EAST COAST EARLY NEXT WEEK...  
   
..PATTERN OVERVIEW AND MODEL ASSESSMENT
 
 
AFTER A BRIEF FLATTENING OF FLOW LATE THIS WEEK, THE PATTERN WILL  
AGAIN AMPLIFY OVER THE LOWER 48 DURING THE MEDIUM RANGE PERIOD.  
THE GEFS AND ECMWF ENSEMBLE MEANS ARE IN AGREEMENT THAT UPPER  
RIDGING ALIGNING OVER THE ROCKIES SHOULD BE SANDWICHED BETWEEN AN  
EXPANSIVE CLOSED LOW OFF THE WEST COAST AND EASTERN U.S. TROUGHING  
BY NEXT WEDNESDAY.  
 
ENSEMBLE MEANS ARE ALSO SHOWING GOOD AGREEMENT WITH SOME OF THE  
SMALLER DETAILS OF THE FORECAST, INCLUDING THE GENERAL EVOLUTION  
OF SHORTWAVE ENERGY AMPLIFYING OVER THE MIDWEST THIS WEEKEND AND  
AN EVENTUAL SURFACE LOW DEEPENING OFF THE CAROLINA COAST EARLY  
NEXT WEEK. HOWEVER, THERE CONTINUES TO BE STARK DIFFERENCES AMONG  
DETERMINISTIC GUIDANCE WITH THE TRACK AND STRENGTH OF THE SURFACE  
LOW. THE GFS HAS BEEN REPRESENTING THE DEEPER AND CLOSER TO COAST  
SIDE OF MODEL SPREAD, WHILE THE ECWMF HAS BEEN ON THE WEAKER AND  
SUPPRESSED EDGE OF THE ENVELOPE OF SOLUTIONS. CONTINUITY,  
ENSEMBLE MEANS, AND ENSEMBLE LOW CLUSTERS ALL WOULD SUPPORT A  
SOLUTION CLOSER TO THE GFS. THE WPC DAY 3-7 FORECAST CONTINUED TO  
RELY HEAVILY ON THE CONSERVATIVE ENSEMBLE MEAN GUIDANCE, BUT THE  
UPDATED BLEND DID RESULT IN SHIFT TOWARDS THE MORE EXTREME GFS. A  
BLEND OF THE ENSEMBLE MEANS ALSO SERVED AS A GOOD STARTING POINT  
OUT WEST, WHERE THERE REMAINS SOME UNCERTAINTY WITH THE DETAILS OF  
AN EXPANSIVE UPPER LOW SETTING UP IN THE NORTHEAST PACIFIC NEXT  
WEEK AND THE ASSOCIATED HEIGHT FALLS AND COLD FRONT EDGING INLAND  
OVER THE WESTERN U.S..  
   
..WEATHER HIGHLIGHTS
 
 
MOISTURE SURGING OUT OF THE GULF OF MEXICO SHOULD FUEL MODERATE TO  
HEAVY PRECIPITATION ALONG AND SOUTH OF A FRONTAL BOUNDARY SETTING  
UP ACROSS THE MIDDLE MISSISSIPPI AND TENNESSEE VALLEYS THIS  
WEEKEND, AND THE CHANCE FOR PRECIPITATION SHOULD SHIFT INTO THE  
MID-ATLANTIC AND SOUTHEASTERN U.S. AS A SURFACE LOW TRACKS FROM  
THE SOUTHERN PLAINS TO THE MID-ATLANTIC COAST. SNOW IS EXPECTED  
WITHIN THE NORTHERN EDGE OF THE DEVELOPING PRECIPITATION SHIELD,  
BUT THE LOCATION AND AMOUNTS REMAIN VERY UNCERTAIN GIVEN THE  
CURRENT MODEL SPREAD WITH POSSIBLE CYCLOGENESIS OFF THE CAROLINA  
COAST EARLY NEXT WEEK. THE LATEST ENSEMBLE GUIDANCE WOULD SUPPORT  
AN AXIS OF ACCUMULATING SNOW EXTENDING FROM THE CENTRAL  
APPALACHIANS TO THE NORTHERN MID-ATLANTIC STATES AND COASTAL AREAS  
OF NEW ENGLAND, BUT AGAIN, THE FORECAST REMAINS UNCERTAIN.  
 
OUT WEST, THERE IS A STRONG SIGNAL FOR A PERIOD OF MODERATE TO  
HEAVY PRECIPITATION ALONG THE TERRAIN OF SOUTHERN CALIFORNIA ON  
SUNDAY AS WEAK SHORTWAVE ENERGY LIFTS THROUGH THE WESTERN U.S. AND  
A HIGHLY ANOMALOUS SURGE OF PACIFIC MOISTURE MOVES INLAND OVER THE  
REGION. ATTENTION FOR PRECIPITATION IN THE WESTERN U.S. WILL  
SHIFT INTO THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA BY THE  
END OF THE FORECAST PERIOD AS A COLD AND HEIGHT FALLS FROM AN  
EXPANSIVE UPPER LOW IN THE NORTHEAST PACIFIC EDGE INLAND ON  
WEDNESDAY.  
 
GERHARDT  
 

 
 
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